A surface acoustic wave device functionally requires a space portion on the surface of a transducer portion that propagates a surface wave. When a layer of foreign matter is formed on the surface of the transducer portion, it adversely affects the propagation of the surface wave and deteriorates the characteristics of the device. To solve this problem, a means for packaging the surface acoustic wave device is used. However, a resin sealing means for use with for example an IC device cannot be used because the resin thereof coats a transducer portion that excites and propagates a surface wave. Thus, conventionally, a sealing means that is so-called an airtightly sealing structure with a metal package or a ceramic package is used.
However, the productivity of the airtightly sealing structure with such a metal package or a ceramic package is low and the surface-mounting density is low.
Prior art references of surface acoustic wave apparatuses that solve such a problem based on a face-down bonding method are known as Japanese Patent Laid-Open Applications No. HEI 4-56510 and No. HEI 5-55303. In these surface acoustic wave apparatuses, a transducer portion and a bonding pad portion are formed on a surface acoustic wave device. A wiring pattern corresponding to the bonding pad portion of the device is formed on the front surface of a board. The bonding pad portion of the device and the wiring pattern of the board are aligned and connected with conductive member such as bump in such a manner that a space portion is formed between the transducer portion and the board. The device is coated and secured by the resin.
As an example of the sealing resin used for fabricating such a surface acoustic wave apparatus, a liquid thermosetting potting type epoxy resin or the like is used. However, since the viscosity of the resin is low, before the resin is hardened, the front surface of the transducer portion is coated with the liquid resin. To prevent this problem, before the device and the board are sealed, a frame-shaped insulation member or dam should be formed on the transducer portion in such a manner that the frame-shaped member or dam surrounds the propagation path of the surface acoustic wave generated by the transducer portion of the device.
Next, with reference to FIG. 46, a conventional surface acoustic wave apparatus will be described. FIG. 46(a) is a sectional view showing the conventional surface acoustic wave apparatus. FIG. 46(b) is a plan view taken along line A-A' of FIG. 46(a). FIG. 46(b) shows a printed circuit board on which a frame-shaped insulation portion is formed. In FIG. 46(b), dashed lines 201 and 202 are imaginary lines denoting a surface acoustic wave device 203 and conductive bumps 204, respectively. In FIG. 46(a), a printed circuit board 205 is composed of an insulation board. Conductive wiring patterns 206 are formed on both surfaces of the insulation board and on edge parts continuing them. A transducer portion 207 that is composed of a comb-shaped electrode pattern and a wiring pattern 208 that is electrically connected to the comb-shaped electrode pattern and supplies a signal are formed on a main surface of the surface acoustic wave device 203. The transducer portion 207 of the surface acoustic wave device 203 and the printed circuit board 205 are disposed in an opposite relation with a space portion 209. The wiring pattern 208 is electrically connected to the wiring patterns 206 on the printed circuit board 205 with conductive bumps 204 composed of Au, Ag, or the like. In addition to the surface acoustic wave device 203, the connected portions of the surface acoustic wave device 203 and the printed circuit board 205 with the conductive bumps 204 are coated with a resin member 210 such as epoxy resin. In this case, as an example of the material of the sealing resin, a liquid thermosetting type epoxy resin is used. In addition, a frame-shaped insulation member or dam 211 is formed on the surface acoustic wave device 203 in such a manner that the frame-shaped insulation member or dam 211 surrounds the surface acoustic wave device 203 so as to prevent the resin 210 from spreading over the space portion 209 before the resin 211 hardens. The frame-shaped insulation member or dam 211 is composed of polyimide resin or the like. In addition, a frame-shaped insulation member or dam 212 is formed on the printed circuit board 205 so as to prevent the resin 210, which coats all or part of the transducer portion 207 of the surface acoustic wave device 203, from spreading from the periphery of the printed circuit board 205. As with the frame-shaped insulation member or dam 211, the frame-shaped insulation member or dam 212 is composed of polyimide resin or the like. FIG. 46(b) is a plan view showing the printed circuit board 205 on which the frame-shaped insulation members or dams 211 and 212 are formed before the surface acoustic wave device 203 is mounted on the printed circuit board.
Thus, the resin 210, which seals the surface acoustic wave device, is blocked by the frame-shaped insulation members or dams 211. Thus, before the resin 210 spreads over the space portion 209, the resin 210 hardens. In other words, the resin 210 does not enter the surface acoustic wave propagation path of the surface acoustic wave device. Thus, since no foreign matter is formed on the front surface of the surface acoustic wave device, the characteristics of the surface acoustic wave device are not deteriorated. In addition, the dam 212 formed at the peripheral portion of the printed circuit board prevents the resin 210 from flowing outside the printed circuit board 205.
However, such frame-shaped insulation members or dams should be formed by a photolithography process using such as photo-sensitive polyimide resin. However, as the number of fabrication steps increases, the fabrication cost rises. Thus, the productivity of the surface acoustic wave apparatus decreases.
In addition, since the frame-shaped insulation members or dams are formed, the effective area of the transducer portion, which is a functional surface of the surface acoustic wave device, should be inevitably reduced. Thus, while there is a growing demand of miniaturization of, for example, an acoustic surface wave apparatus for mobile communication, the characteristics and functions of the surface acoustic wave apparatus cannot be satisfactorily obtained. Moreover, a study conducted by the inventors of the present invention reveals that even if such frame-shaped insulation members or dams are formed with the conventional liquid sealing resin, the resin slightly leaks out from a gap of the frame-shaped insulation members or dams due to the capillarity effect and thereby the resin reaches the transducer portion, which is the surface acoustic wave propagation path. Thus, the yield of the fabrication decreases.